1. Field of Invention
Embodiments of the present invention relate generally to a system and a method for supporting a web in a polishing system.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
CMP systems generally include a polishing head, a platen and polishing material disposed on the platen. A substrate retained in the polishing head is pressed against the polishing material and moved relative to the polishing material in the presence of a polishing fluid. Abrasives, typically contained in the polishing fluid or polishing material, remove material from the surface of the substrate synergistically with the chemical activity provided by the polishing fluid.
One type of polishing material that includes abrasives disposed therein is known as fixed abrasive material. The fixed abrasive material comprises a plurality of abrasive particles suspended in a resin binder that is disposed in discrete elements on a backing sheet. As the abrasive particles are contained in the polishing material itself, systems utilizing fixed abrasive material generally use polishing fluid that do not contain abrasives. Such polishing fluids enhance the service life of their fluid delivery systems.
Fixed abrasive polishing material is generally available in stick-down form but is often utilized in the form of a web. Generally, the web is periodically advanced over the course of polishing a number of substrates as the polishing surface of the web is consumed by the polishing process. A vacuum is typically applied between the web and platen to fix the web to the platen during the polishing process. When the web is advanced, the vacuum is removed, freeing the web from the platen""s surface.
However, indexing the web across a polishing platen is sometimes difficult. Fluids that come in contact with the web may cause surface tension or attraction to develop between the web and the underlying surface of the platen.
This surface tension must be over-come to accomplish advancement of the web. If the attraction between the web and platen is great, the indexing means may not be able to index the web or the web may become damaged during the indexing process.
Providing a cushion of gas between the web and platen assists in overcoming the attraction between the web and platen. The gas lifts the web to a spaced-apart relation to the platen where the web may be freely indexed. However, providing gas to the area between the web and platen is complicated, and requires rotary union and process tubing to be routed through an already crowded platen.
Therefore, there is a need for an improved apparatus that supports a web of polishing material.
One aspect of the invention generally provides an apparatus for supporting a web of polishing material. In one embodiment, the apparatus includes a platen adapted to support the web, a frame assembly, and one or more flexures coupled between the platen and the frame assembly. The frame assembly may be actuated to lift the web into a space-apart relation relative to the platen.
In another aspect of the invention, method for supporting a web of polishing material is provided. In one embodiment, the method includes the steps of supporting a web across a frame at least partially circumscribing a platen and moving the frame assembly in relation to the platen. In one position, the frame assembly places the web in a space-apart relation relative to the platen.
In another aspect of the invention, an apparatus for tensioning a web of polishing material between a supply roll and a take-up roll is provided. In one embodiment, the apparatus includes a first drive adapted to pull the polishing material in a first direction, a clutch mechanism coupled to the first drive, and a second drive adapted to pull the polishing material in a second direction that opposes the first direction.
In another aspect of the invention, a method for tensioning a web of polishing material between a supply roll and a take-up roll is provided. In one embodiment, the method includes the steps of driving a first motor to urge the polishing material in a first direction, and driving a second motor to urge the polishing material in a second direction that opposes the first direction. In another embodiment, a method for tensioning includes the steps of disposing the web across a polishing platen having a guide supporting the web at one end of the platen, disposing a first sensor between the platen and one end of the guide, disposing a second sensor between the platen and another end of the guide, and generating a signal from the first and second sensors that is indicative of web tension.